1. Technical Field
This disclosure relates to an image forming apparatus including a liquid discharge head unit.
2. Description of the Background
One example of related-art image forming apparatuses having two or more of printing, copying, plotting, and facsimile functions includes a liquid discharge device including a recording head. The recording head includes a liquid discharge head configured to discharge droplets of a recording liquid such as ink. The ink discharged from the recording head adheres to a recording medium, such as a sheet, while the sheet is conveyed so that an image is formed on the sheet.
An image forming apparatus hereinafter described forms an image on a recording medium, such as paper, string, fiber, cloth, lather, metal, plastics, glass, wood, and ceramics by discharging a liquid onto the recording medium. An image hereinafter described refers to a significant image such as characters and figures, as well as a non-significant image such as patterns. A liquid hereinafter described is not limited to a recording liquid and ink, but also includes a material which is a liquid when discharged from a recording head, such as a DNA sample, a resist material, and a pattern material. A liquid discharge device hereinafter described is a device configured to discharge the liquid from a liquid discharge head, as well as a device configured to form the image.
During, before, and after discharging the liquid (hereinafter referred to as ink), liquid chambers and a common liquid chamber of the liquid discharge head are required to be filled with the ink without bubbles to reliably discharge the liquid.
However, because the liquid discharge head is filled with air before being initially filled with the ink, bubbles are easily included in the ink during the initial filling operations. Moreover, a larger amount of air enters the liquid chambers and the common liquid chamber from a nozzle due to application of a large amount of negative pressure and other factors, causing bubbles in the ink.
It is required to surely remove the air in the liquid chambers and the common liquid chamber and the bubbles in the ink in order to reliably discharge the ink from the liquid discharge head. Particularly, in a case in which a long liquid discharge head such as a line-type liquid discharge head is used to increase a printing speed, a longer common liquid chamber is required so that pressure loss of the ink in the common liquid chamber increases. Consequently, a speed of flow of the ink decreases severely at a portion farthest from an ink supply opening of the common liquid chamber, and bubbles and other foreign materials tend to remain at that portion, possibly causing improper discharge of the ink.
To solve the above-described problems, a liquid discharge head including a circulation supply system in which a common liquid chamber does not have components to block a flow of ink has been proposed. For example, Japanese Patent No. (hereinafter referred to as JP) 3090698 discloses an inkjet recording device including a first flow path configured to connect a recording head and an ink tank, in which an ink supply unit for supplying ink from the ink tank to the recording head is provided, a second flow path configured to connect the recording head and the ink tank, in which a first backflow prevention unit for preventing the ink from flowing to the recording head from the ink tank is provided, and a third flow path configured to connect the ink tank and a portion between the ink supply unit and the recording head, in which a second backflow prevention unit for preventing the ink from flowing to the ink tank from the recording head is provided.
The above-described inkjet recording device is described in detail below with reference to FIG. 1. First, a pump 503 is normally rotated while a check valve 501 is opened and a check valve 502 is closed so that ink is supplied to a recording tank 504 from a main tank. Subsequently, the pump 503 is reversely rotated while the check valves 501 and 505 are closed and the check valve 502 is opened so that the ink flows to the check valve 502, a flow path 506, a filter 507, a common liquid chamber 508, a flow path 509, an electromagnetic valve 510, and the recording tank 504 in this order, as indicated by a dashed arrow in FIG. 1. Meanwhile, during image formation, the electromagnetic valve 510 is closed and the ink is supplied to a liquid path 512 from the recording tank 504 through a liquid path 511, the liquid path 506, the filter 507, and the common liquid chamber 508 in this order, as indicated by a virtual arrow in FIG. 1 so that ink droplets are discharged from a nozzle 513. The recording tank 504 includes a release valve 515.
Other examples of inkjet recording devices and image recorders are also disclosed in JP 3885226 and published unexamined Japanese Patent application Nos. (hereinafter referred to as JP-As) 2006-068904, 2006-088493, 03-213350, 02-179757, and 05-008400.
However, the above-described examples do not fully solve the problems. For example, in the inkjet recording device disclosed in JP 3090698, the flow path used for filling the recording head with the ink is separately provided from the flow path used for recording. Consequently, the inkjet recording device needs a more complicated configuration. Moreover, a large number of check valves and electromagnetic valves is needed, causing cost increase and requiring more complicated control operations.